As illustrated in FIG. 66, for example, the related-art bearing device for a wheel includes, as main components thereof, a constant velocity universal joint 107, and a wheel bearing 106 including a hub wheel 101, an inner ring 102, double-row balls 103 and 104, and an outer ring 105.
The hub wheel 101 has an inner raceway surface 108 on an outboard side formed on an outer peripheral surface thereof, and includes a wheel mounting flange 109 for allowing a wheel (not shown) to be mounted thereto. Hub bolts 110 for fixing a wheel disc are equiangularly embedded in the wheel mounting flange 109. The inner ring 102 is fitted to a small-diameter step portion 111 formed on an outer peripheral surface of the hub wheel 101 on an inboard side, and an inner raceway surface 112 on the inboard side is formed on an outer peripheral surface of the inner ring 102. On an inner peripheral surface of a shaft hole of the hub wheel 101, a female spline 113 for coupling the constant velocity universal joint 107 to allow torque transmission therebetween is formed.
The inner ring 102 is press-fitted with adequate interference for the purpose of preventing creep. The inner raceway surface 108 on the outboard side that is formed on the outer peripheral surface of the hub wheel 101 and the inner raceway surface 112 on the inboard side that is formed on the outer peripheral surface of the inner ring 102 constitute double-row inner raceway surfaces. The inner ring 102 is press-fitted into the small-diameter step portion 111 of the hub wheel 101, and an end portion of the small-diameter step portion 111 is crimped outward. As a result, the inner ring 102 is retained by a crimped portion 114 thus formed and integrated with the hub wheel 101, to thereby apply preload to the wheel bearing 106.
The outer ring 105 has double-row outer raceway surfaces 115 and 116 formed on an inner peripheral surface thereof and opposed to the inner raceway surfaces 108 and 112 of the hub wheel 101 and the inner ring 102. The outer ring 105 has a vehicle body mounting flange 117 for mounting the wheel bearing 106 to a vehicle body (not shown) on an outer peripheral surface thereof. The vehicle body mounting flange 117 is fixed to a knuckle extending from a suspension device (not shown) of the vehicle body with a bolt or the like by using a mounting hole 118.
The wheel bearing 106 has a double-row angular ball bearing structure. That is, the balls 103 and 104 are interposed between the inner raceway surfaces 108 and 112 formed on the outer peripheral surfaces of the hub wheel 101 and the inner ring 102 and the outer raceway surfaces 115 and 116 formed on the inner peripheral surface of the outer ring 105. Then, the balls 103 and 104 in respective rows are equiangularly supported by cages 119 and 120.
At opening portions on both ends of the wheel bearing 106, a pair of seals 121 and 122 for sealing annular spaces between the outer ring 105 and the hub wheel 101 and between the outer ring 105 and the inner ring 102 are fitted to the inner diameter at both end portions of the outer ring 105. With this, leakage of lubricant such as grease filled inside and entrance of water and foreign matter from the outside are prevented.
The bearing device for a wheel is configured by coupling an outer joint member 123 of the constant velocity universal joint 107 to the hub wheel 101. The outer joint member 123 includes a cup-shaped mouth section 124 that accommodates internal components (not shown) such as an inner joint member, balls, and a cage, and a stem section 125 that integrally extends from the mouth section 124 in an axial direction. On an outer peripheral surface of the stem section 125, a male spline 126 for coupling the stem section 125 to the hub wheel 101 to allow torque transmission therebetween is formed.
The stem section 125 of the outer joint member 123 is press-fitted into the shaft hole of the hub wheel 101 so that a nut 127 is threadedly engaged with a male thread portion 129 formed at an end portion of the stem section 125. Then, by fastening the nut 127 in a state of being locked to an end surface of the hub wheel 101, the constant velocity universal joint 107 is fixed to the hub wheel 101. A shoulder portion 128 of the outer joint member 123 is brought into abutment against the crimped portion 114 of the hub wheel 101 by a fastening force (axial force) of the nut 127. In this manner, the male spline 126 of the stem section 125 and the female spline 113 of the hub wheel 101 are fitted to each other. As a result, the torque transmission from the constant velocity universal joint 107 to the wheel bearing 106 is enabled.
In the bearing device for a wheel described above, the crimped portion 114 of the hub wheel 101 and the shoulder portion 128 of the outer joint member 123, which is opposed to the crimped portion 114, are in a state of abutment against each other by the fastening force (axial force) of the nut 127. Thus, when a rotational torque is applied from the constant velocity universal joint 107 to the wheel bearing 106 that is in a stationary state at the start of the vehicle, the rotational torque is to be transmitted from the outer joint member 123 to the hub wheel 101 through an intermediation of the female spline 113 and the male spline 126. At this time, however, sudden slippage occurs between the crimped portion 114 of the hub wheel 101 and the shoulder portion 128 of the outer joint member 123 due to torsion of the outer joint member 123. Stick-slip noise generally referred to as squeaking noise is sometimes generated due to the sudden slippage.
As means for preventing the stick-slip noise, means for increasing a frictional resistance on contact surfaces of the crimped portion 114 of the hub wheel 101 and the shoulder portion 128 of the outer joint member 123 has been taken so as not to cause the sudden slippage (see Patent Literature 1, for example). In Patent Literature 1, there are disclosed, as the means for increasing the frictional resistance, a structure in which radial, oval, or cross-hatched projecting and depressed portions are formed on the contact surface of the shoulder portion 128 of the outer joint member 123 and a structure in which a spacer made of rubber or resin is provided on the contact surface of the shoulder portion 128 of the outer joint member 123.
Further, as another means for preventing the stick-slip noise, means for reducing the frictional resistance on the contact surfaces of the crimped portion 114 of the hub wheel 101 and the shoulder portion 128 of the outer joint member 123 has been taken so as not to cause the sudden slippage (see Patent Literature 2, for example). In Patent Literature 2, there is disclosed a structure in which a depressed groove is formed on the contact surface of the crimped portion 114 of the hub wheel 101 and the depressed groove is filled with grease.